1. Field of the Invention
The present invention relates to a method to control a sleep operation of an air conditioner, and more particularly, to a method to control a sleep operation of an air conditioner in which an indoor temperature is automatically changed in the sleep operation to allow the user to sleep soundly.
2. Description of the Related Art
A conventional air conditioner performs cooling and heating operations to cool and heat indoor air to keep it at a target indoor temperature selected by the user, thereby providing a comfortable room environment to the user. However, when the user sleeps during the cooling operation, they feel cold after a certain time elapses from the start of the cooling operation since the air conditioner operates with only the initially set target indoor temperature throughout the cooling operation and feel hot if the cooling operation is turned off, thereby failing to provide a comfortable sleep environment. On the other hand, when the user sleeps during the heating operation, they feel hot after a certain time elapses from the start of the heating operation since the air conditioner operates with only the initially set target indoor temperature throughout the heating operation and feel cold if the heating operation is turned off, thereby failing to provide a comfortable sleep environment.
FIG. 1 illustrates the characteristics of sleep states in which non-REM and REM sleep periodically alternate. As shown in FIG. 1, every human being alternately undergoes non-REM and REM sleep 4 or 5 times at intervals of about 90 minutes in a night. It can be seen from FIG. 1 that the deepest sleep is a non-REM sleep immediately after they fall asleep. The cold or hot feeling and the metabolic rate of the human being depend on the amount of heat generated from the skin. The human being feels colder as the metabolic rate decreases. FIG. 2 illustrates the characteristics of changes in the metabolic rate of human beings until they wake up after falling asleep. After they fall asleep, the metabolic rate of human beings is reduced to make them fall into a non-REM sleep as shown in FIG. 2. When they fall into a deep sleep from a shallow sleep, the body temperature of human beings is significantly reduced, causing serious perspiration. The perspiration causes the human being to feel hot and uncomfortable, thereby making it difficult to fall into a deep sleep.
To overcome these problems, Japanese Patent Application Publication No. 2004-92918 suggested an air conditioner which reduces the indoor temperature to be lower than a target indoor temperature set by the user at an initial stage in a preset sleep operation duration to allow them to quickly fall asleep, taking into consideration the sleep state characteristics of FIG. 1 and the changes in the metabolic rate of human beings during sleep. When the user has fallen asleep, their metabolic rate and activity is reduced so that they easily feel cold. Therefore, after the user falls asleep, the air conditioner gradually increases the indoor temperature to allow the user to sleep soundly.
However, this conventional method to control a sleep operation of an air conditioner does not take into consideration the sleep operation duration desired by the user and performs sleep operation control based on 8 hours which is the average sleep time, thereby failing to achieve efficient sleep operation control.
In addition, in the intermediate and final stages of the sleep operation, the indoor temperature becomes higher than the preset target temperature to increase the skin temperature of the user, thereby disturbing their sound sleep.
Further, the conventional air conditioner provides the sleep operation only for cooling, thereby failing to satisfy the user's desire for the sleep operation for heating.